Administrator Guide

Table Of Contents
If you enable IGMP snooping, IGMP queries are also sent out on the VLT ports at this time allowing any receivers to respond to
the queries and update the multicast table on the new node.
This delay in bringing up the VLT ports also applies when the VLTi link recovers from a failure that caused the VLT ports on the
secondary VLT peer node to be disabled.
PIM-Sparse Mode Support on VLT
The designated router functionality of the PIM Sparse-Mode multicast protocol is supported on VLT peer switches for multicast
sources and receivers that are connected to VLT ports.
VLT peer switches can act as a last-hop router for IGMP receivers and as a first-hop router for multicast sources.
Figure 115. PIM-Sparse Mode Support on VLT
On each VLAN where the VLT peer nodes act as the first hop or last hop routers, one of the VLT peer nodes is elected as the
PIM designated router. If you configured IGMP snooping along with PIM on the VLT VLANs, you must configure VLTi as the
static multicast router port on both VLT peer switches. This ensures that for first hop routers, the packets from the source are
redirected to the designated router (DR) if they are incorrectly hashed. In addition to being first-hop or last -hop routers, the
peer node can also act as an intermediate router.
On a VLT-enabled PIM router, if any PIM neighbor is reachable through a Spanned Layer 3 (L3) VLAN interface, this must be
the only PIM-enabled interface to reach that neighbor. A Spanned L3 VLAN is any L3 VLAN configured on both peers in a VLT
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Virtual Link Trunking (VLT)